Blue

Consider the color blue.
Is the color blue I see the same color blue that you see? Perhaps the color you percieve as blue is the color I percieve as your
orange. We both call it blue. I could say object A is blue and you would agree. However if you switch bodies with me and look at the same object you would say it was orange. Now since we currently have no method of switching bodies we will never be able to know how similar my reality is to your reality.

It's all about perception.